Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant, which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc
Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from major deficiencies such as poor image stability against light and gases commonly contained in the air, such as ozone (O3), nitrogen oxide (NOx) and sulfur oxide (SOx), especially on receivers having porous ink receiving layers. One method of addressing these limitations is to use pigment-based inks. When designed properly, pigment based inks usually can demonstrate image stability significantly higher than the dye based inks, and more importantly, approaching the archival quality as compared to silver halide photographic prints.
A major image quality drawback of pigment-based inks is “inter-color differential gloss”, where the gloss levels of imaged areas of different colors are very different from each other. This type of image quality defect can be quite noticeable, even to ordinary observers. One possible solution to this problem is to cover the entire receiver with a protective layer through techniques such as laminating the printed image, or fusing the top fusible polymeric layer in receivers to a continuous overcoat layer, such as those disclosed in U.S. patent application, Ser. No.09/954,779, filed on Sep. 18, 2001 of Wexler, or coating a protective layer on the imaged areas as described in EP1057646 and EP1048466. However, all these approaches involve separate steps after printing, making the entire process complex and costly.
What the art needs is a way to minimize gloss level variations among different colors in a color image when the various inks are deposited and dried on a receiver. This should be done as part of the printing process and not as a separate step after printing.